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Message-Id: <777DD215-A4F5-454F-856F-FFE870F15CDD@amacapital.net>
Date: Fri, 1 Feb 2019 14:36:24 -0800
From: Andy Lutomirski <luto@...capital.net>
To: Thomas Garnier <thgarnie@...omium.org>
Cc: Andy Lutomirski <luto@...nel.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Kristen Carlson Accardi <kristen@...ux.intel.com>,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>,
X86 ML <x86@...nel.org>, Masahiro Yamada <yamada.masahiro@...ionext.com>,
Juergen Gross <jgross@...e.com>, Joerg Roedel <jroedel@...e.de>,
Jia Zhang <qianyue.zj@...baba-inc.com>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Tim Chen <tim.c.chen@...ux.intel.com>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 20/27] x86: Support global stack cookie
> On Feb 1, 2019, at 12:21 PM, Thomas Garnier <thgarnie@...omium.org> wrote:
>
>> On Fri, Feb 1, 2019 at 11:27 AM Andy Lutomirski <luto@...nel.org> wrote:
>>
>>> On Thu, Jan 31, 2019 at 11:29 AM Thomas Garnier <thgarnie@...omium.org> wrote:
>>>
>>> Add an off-by-default configuration option to use a global stack cookie
>>> instead of the default TLS. This configuration option will only be used
>>> with PIE binaries.
>>>
>>> For kernel stack cookie, the compiler uses the mcmodel=kernel to switch
>>> between the fs segment to gs segment. A PIE binary does not use
>>> mcmodel=kernel because it can be relocated anywhere, therefore the
>>> compiler will default to the fs segment register. This is fixed on the
>>> latest version of gcc.
>>
>> I hate all these gcc-sucks-so-we-hack-it-and-change-nasty-semantics
>> options. How about just preventing use of both stack protector and
>> PIE unless the version of gcc in use is new enough.
>
> So fail the build in this scenario?
Fail the build or use some Kconfig magic to prevent this from being configured in the first place.
>
>>
>> Also, does -mstack-protector-guard-reg not solve this? See
>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81708. Or is there
>> another bug? Or are you worried about gcc versions that don't have
>> that feature yet?
>
> I am worried about gcc versions that don't have this feature, yes.
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